The History of Pressure Measurement: From Mercury Tubes to Microchips

A technician today can pull a device from their pocket, connect a tube, and instantly read a precise measurement of an invisible force—air pressure. We see this force’s effects everywhere, from the weather report’s barometric pressure to the inflation of our tires. But how did we learn to measure something we cannot see, touch, or hold? The story of the manometer is a multi-century journey of scientific curiosity, industrial necessity, and engineering genius, taking us from towering columns of liquid to microscopic whispers on a silicon chip.

Act I: The Eloquence of Liquids (17th Century)

Our story begins in a time when the prevailing wisdom, inherited from Aristotle, was that “nature abhors a vacuum.” In the 1640s, an Italian physicist named Evangelista Torricelli challenged this idea. He filled a long glass tube, sealed at one end, with mercury and inverted it into a dish of mercury. The column of mercury in the tube fell, but only to a height of about 76 centimeters, leaving a void at the top. Torricelli correctly reasoned that this wasn’t an imperfect vacuum, but that the immense weight of the Earth’s atmosphere was pressing down on the mercury in the dish, balancing the weight of the mercury column in the tube. He had invented the barometer.

This was a profound conceptual leap. The “empty” air had weight and exerted pressure. This principle was quickly adapted into the U-tube manometer. Imagine a simple U-shaped tube partially filled with water. If you apply pressure to one side—by blowing into it, for example—the water level on that side goes down, and the level on the other side goes up. The difference in height between the two columns is a direct, visual measurement of the pressure you applied. For the first time, this unseen force was made elegantly visible, its story told by the simple eloquence of a liquid.

Act II: The Dance of the Brass Tube (19th Century)

For two centuries, liquid manometers were the gold standard. But as the Industrial Revolution roared to life, a new world of high-pressure steam engines and boilers demanded a more robust, compact, and safe way to measure pressure. A tall, fragile glass tube of mercury was no match for the vibrating, high-pressure heart of a locomotive.

The solution came in 1849 from a French engineer named Eugène Bourdon. His invention, the Bourdon tube, was a masterpiece of mechanical simplicity. He took a tube with an oval cross-section and bent it into a C-shape. When pressure was applied to the inside of this tube, the oval cross-section tried to become more circular, causing the entire C-shape to straighten out slightly. It’s the same principle as a coiled-up party blower that unfurls when you blow into it.

Bourdon connected the moving end of this tube to a series of levers and gears, which amplified the tiny movement and translated it to the rotation of a pointer on a calibrated dial. The Bourdon gauge was born. It was rugged, cheap, and reliable. It became the face of pressure measurement for over a century, seen everywhere from factory floors to a doctor’s office, its needle performing a quiet, mechanical dance in response to the unseen force within.

Act III: The Whisper of Silicon (20th Century)

The next great leap required moving from the world of mechanical motion to the invisible realm of electrons. The stage shifted to Bell Labs in the 1950s, a hotbed of research into semiconductor materials like silicon. In 1954, a scientist named Charles S. Smith was studying the electrical properties of silicon and discovered something remarkable: when he physically squeezed or stretched a piece of silicon, its electrical resistance changed significantly. He had discovered the piezoresistive effect.

The implication was immense, though it took decades of micro-fabrication technology to fully realize. Imagine a microscopic silicon diaphragm, thinner than a human hair, etched onto a chip. When pressure is applied, this diaphragm flexes by an infinitesimal amount. Bonded to this diaphragm are piezoresistive elements. As the diaphragm bends, these resistors are stretched, changing their resistance. The chip’s circuitry can measure this change with incredible precision and translate it directly into a digital pressure reading.

This was the birth of the modern solid-state pressure sensor. There are no moving parts, no liquids, no gears—just the subtle whisper of a silicon wafer responding to force.

Epilogue: From Monumental to Miniature

From Torricelli’s meter-high tube of mercury, to Bourdon’s brass gauge, to a sensor smaller than a fingernail—the journey has been one of relentless miniaturization and increasing precision. This evolution allows a modern digital manometer, like a Fieldpiece SDMN5, to be a handheld, battery-powered device that is more accurate and sensitive than even the most carefully constructed laboratory instruments of the past.

The next time you see a technician check the pressure in an HVAC system, remember the long chain of thought and invention that fits into the palm of their hand: the scientific courage of Torricelli, the mechanical ingenuity of Bourdon, and the quantum-level discovery of Smith, all converging to give us a clear voice for the unseen forces that shape our world.